Compositions having isocyanate functional components are utilized to bond substrates together, such as, glass, often in the form of windows, into structures. In automotive assembly plants windows are often bonded in with one part adhesive compositions containing isocyanate functional components. These compositions cure by reaction with ambient moisture. One part adhesives are used because the equipment required to dispense and apply them is less complex than the equipment used to apply two-part adhesives. One part moisture curing adhesives typically take several hours to cure. In the assembly plants, vehicles are not driven for several hours and this is acceptable. One part moisture curing adhesives known in the art are disclosed in U.S. Pat. Nos. 4,374,237; 4,687,533; 4,780,520; 5,063,269; 5,623,044; 5,603,798; 5,852,137; 5,922,809; 5,976,305; 5,852,137 and 6,512,033, relevant portions incorporated herein by reference. Examples of commercial one part adhesives include BETASEAL™ 15630, 15625, 61355 adhesives available from The Dow Chemical Company, EFBOND™ windshield adhesives available from Eftec, WS 151™, WS212™ adhesives available from Yokohama Rubber Company, and SIKAFLEX™ adhesives available from Sika Corporation.
Two-part compositions containing isocyanate functional prepolymers in one part and compounds having isocyanate reactive components in the other part are used where cure speed is important, such as in the automotive aftermarket replacement glass business. Customers desire that the adhesives cure quickly so that the vehicle can be driven as soon as possible after replacing the window. The advantage is that two-part adhesive cure at much faster reaction rates than one part moisture curing adhesives Examples of two-part compositions containing isocyanate functional prepolymers in one part and compounds having isocyanate reactive components in the other part are disclosed in EP 1,524,282, U.S. Pat. Nos. 5,852,103; 6,709.539; 7,101,950 and 7,361,292, relevant parts incorporated herein by reference.
Adhesives are utilized in a variety of environments and the properties required are different. Adhesive systems that allow for modification of properties to fit the environment of use or the substrates bonded are desired. Modification of the relative elasticity and modulus of adhesive is desirable. Manufacturers desire to handle products as soon as possible to enhance productivity. In modern industrial processes, there is a need to move parts and to place loads on adhesive systems as soon as possible. Adhesives which have a good green strength shortly after application are needed. Typical one part adhesives do not provide such green strength properties. Adhesive systems need a longer open time, the time from application of the adhesive to a substrate until the adhesive can no longer adhere to a substrate, than two-part adhesives allow. Open times 8 minutes to 15 minutes is desired.
Some processes used to assemble parts using reactive adhesives require cleaning of the substrate surface to remove contaminants. A primer or activator may be utilized to facilitate adhesion to the substrate. A primer or activator system may contain a film forming resin, a solvent and one or more of an adhesion promoter, catalyst; curing agent or crosslinking agent, see for example DE 19924139. In most commercial applications; primers require a minimum amount of time between application of the primer and application of the adhesive to allow % film build up. If adhesives are applied before the minimum time, the primer may not form a coherent film and there is a risk that the primer will not bond to the substrate or the adhesive surface. Many primers are moisture cure primers which require the presence of moisture to form an adequate film. Examples of primers are U.S. Pat. Nos. 5,115,086; 5,238,993; 5,466,727; 5,468,317; and 5,792,811, all incorporated herein by reference. Non-film forming solutions of adhesion promoters, often called activators, are used which may contain groups intended for reaction with the substrate and the adhesive. Examples of wipe systems include U.S. Pat. No. 6,053,971, incorporated herein by reference. Examples of adhesion promoters useful are silanes, isocyanate containing compounds, titanates and zirconates such as disclosed in U.S. Patent Publications 2005/0126683 and 2006/0124225, all incorporated herein by reference. The use of primers require process steps to apply the primer, provide two additional surfaces along which an adhesive system can fail and add process time to manufacturing processes. Moving parts or articles bonded together with adhesives or placing a load on the adhesive bond before the system builds adequate strength can result in failure of the adhesive system thus resulting in faulty parts or articles. Commonly owned application titled IMPROVED PROCESS FOR BONDING REACTIVE ADHESIVES TO SUBSTRATES published as WO 2010/030519 discloses a system, or kit, comprising i) a stable solution or dispersion of a catalyst for the curing of a reactive adhesive system; and in a separate part ii) an uncured reactive adhesive system wherein the catalyst of part i) accelerates the cure of the reactive adhesive system. This system improves the speed of link up of an adhesive to a substrate.
Thus, what are needed are adhesive systems which exhibit good green strength, rapid cure rates and the ability to allow substrates to be handled shortly after application of the adhesive system. What are also needed are adhesive systems wherein the properties can be adjusted to meet the needs of a particular substrate system.